The longterm objective of this proposal is the continued investigation of macular retinal microvascular circulation in man using the noninvasive blue field simulation technique. Macular leukocyte flow and reactivity to breathing 100% oxygen will be examined in diabetic eyes as follows: la Eyes with varying types of diabetic maculopathy In a cross-sectional study of type one diabetics, leukocyte hemo- dynamics will be measured in diabetic eyes without microangiopathy and in eyes with specific maculopathy lesions. The results will be compared with measurements in eyes of age and sex matched normal individuals. Secondary objectives will be to investigate within the diabetic eyes with no microangiopathy, the effect on the microvascular circulation of (1) duration of diabetes, (2) blood glucose taken at the time of measurement, (3) glucose control as assessed by HgAlC and (4) peripheral leukocyte count. lb Eyes of patients after induction of acute hyperglycemia Alterations of macular retinal capillary blood flow and vascular reactivity will be examined in eyes of type one diabetic patients with mild diabetic retinopathy before and two hours following an oral glucose induction of hyperglycemia. lc Eyes undergoing macular focal argon photocoagulation for foveal edema and/or exudate. Macular leukocyte flow and microvascular hemodynamics will be measured in eyes before and following macular photocoagulation for diabetic macular edema and/or exudate to determine if changes occur and are associated with changes in the edema. These studies will provide new and unique information on the microvascular hemodynamic alterations which occur in the macula of diabetic eyes and should give insight into the mechanisms contributing to retinal vascular leakage, edema and exudate as well the effect of photocoagulation treatment. If changes are produced in the hemodynamics with acute elevation of blood sugar, this will provide significant insight into the mechanisms involved in development and progression of microangiopathy and will provide a potent tool to evaluate intervention.